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Charge a battery in just six minutes

By Duncan Graham-Rowe

Electrode upgrade

A rechargeable battery that can be fully charged in just 6 minutes, lasts 10 times as long as today’s rechargeables and can provide bursts of electricity up to three times more powerful is showing promise in a Nevada lab.

New types of battery are badly needed. Nokia’s chief technologist Yrjö Neuvo warned last year that batteries are failing to keep up with the demands of the increasingly energy-draining features being crammed into mobile devices (New Scientist print edition, 28 February 2004).

The highest energy-per-weight ratio in today’s batteries is provided by lithium-ion (Li-ion) batteries. They are also cheaper in terms of energy delivered per unit of weight than alternative types of battery such as nickel-metal-hydride (NiMH) and nickel-cadmium (Ni-Cd) types. But Li-ion cells have their drawbacks too. They eventually wear out, and they cannot discharge energy quickly enough for applications requiring power surges, such as camera flashguns and power tools.

They may soon be able to. Altair Technologies of Reno has created a new type of Li-ion cell in which the anode has an exceptionally high surface area. This allows electrons to enter and leave it quickly – making fast recharging possible and providing high currents when needed.

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Chemical tricks

Li-ion batteries work by forcing lithium ions from a lithium cobalt oxide cathode to migrate to a carbon anode via an electrolyte solution. Altair’s patented modification is to make the anode surface out of lithium titanate nanocrystals, using chemical tricks to give it a surface area of about 100 square metres per gram, compared with 3 square metres per gram for carbon.

The firm is keeping the chemistry that allows it to do this pretty close to its chest for commercial reasons. But the patent (US 6689716) reveals that the increased surface area is achieved using a carefully controlled sequence of evaporative steps when making the lithium titanate crystals.

The high current that this modified electrode is able to carry means power-hungry devices can be installed in mobile phones, which until now have been denied them. For instance, camera phones might now have enough power to run a flashgun.

Longer lifespan

Altair says the battery will have other advantages, too. The crystalline surface of a carbon anode is susceptible to damage by the repeated temperature changes that occur as the battery is used and recharged. This limits its life to around 400 charging cycles.

The more rugged lithium titanate anode should make it possible to recharge the battery as many as 20,000 times says Roy Graham, development director at Altair. A longer lifespan should also be better for the environment, he says. “The continual use of polluting cobalt oxides is questionable.”

Altair plans to develop its batteries for power tools, which have till now required more expensive Ni-Cd or NiMH batteries to provide the large currents these devices need. The company hopes to license its technology to major battery-makers, who could have the device on the market in two years’ time. Altair says it eventually wants to produce batteries for a broad range of devices, from phones to hybrid electric vehicles.